Passive and active millimeter-wave imaging systems for a variety of applications are known. A comprehensive review of architectures of passive millimeter-wave (MMW) imaging systems is given for example in a paper by Alan H Lettington et al. 2003, J. Opt. A: Pure Appl. Opt. 5, S103-S110. The paper includes sources of radiation, atmospheric transmission, various types of available imaging system and a brief summary of exemplary applications. Specific issues related to detection capabilities provided by active imaging systems and a comparison between imaging with focal plan array antennae versus scanning an image by a single pixel are discussed for example in a paper of E. N. Grossman and A. J. Miller, 2003, Proceedings of SPIE, Vol. 50277, pp 62-70. Typically such systems consist of components such as lenses for optical beam forming and employ mechanical beam steering. However MMW lenses are somewhat impractical in cases in which the required range of detection, or the range to the target to be imaged, exceed a few meters. Therefore, an improved converging optics is called for.